Related Stories

Scientists have worked out a new way to measure the mass of a planet using pulsars.

The new technique will help in the hunt for the much sought-after but elusive gravitational wave.

Reporting in the Astrophysical Journal, an international research team lead by Australia's CSIRO says the new weighing technique is sensitive to just 0.003% of the mass of the Earth, and one ten-millionth the mass of Jupiter.

Dr Dick Manchester from CSIRO Astronomy and Space Science says scientists need to know a planet's mass because it interferes with pulsar signals, used in the search for gravitational waves. Pulsars are rapidly spinning neutron stars.

A new technique

At the moment planets are weighed by measuring how their gravity affects things like moons or spacecraft orbiting around them.

But by using the distortions in pulsar signals as a guide, researchers can tell if their planetary mass measurements are out, and if so, by how much.

So if the wrong mass is given for Jupiter, a regular patter of pulsar timing errors will show up. But once the right mass is entered, the errors disappear.

Manchester says data from four pulsars has been used to weigh Mercury, Venus, Mars, Jupiter and Saturn complete with moons and rings.

"Most of the data was recorded by CSIRO's Parkes radio telescope, with Germany's Effelsberg telescope and the Arecibo radio telescope in Puerto Rico also contributing," he says.

Gravitational waves

Gravitational waves were first predicted by Albert Einstein. According to General Relativity theory, a gravitational wave is a fluctuation in the curvature of space-time which propagates as a wave travelling out from a source such as a black hole or binary star system.

Interferometer observatories on Earth built to find these waves have so far failed, and pulsars are seen as an alternative method.

But finding these waves depends on spotting minute changes in the timing of pulsar signals, and so all other sources of timing error must be accounted for, including the traces of solar system planets.

The new weighing technique will also help future missions using gravity assist to slingshot spacecraft around planets and moons to build up speed for their journey.